Apparatus and methods for ion beam implantation

ABSTRACT

This invention discloses an ion implantation apparatus with multiple operating modes. It has an ion source and an ion extraction means for extracting a ribbon-shaped ion beam therefrom. The ion implantation apparatus includes a magnetic analyzer for selecting ions with specific mass-to-charge ratio to pass through a mass slit to project onto a substrate. Multipole lenses are provided to control beam uniformity and collimation. The invention further discloses a two-path beamline in which a second path incorporates a deceleration system incorporating energy filtering. The invention discloses methods of ion implantation in which the mode of implantation may be switched from one-dimensional scanning of the target to two-dimensional scanning, and from a simple path to an s-shaped path with deceleration.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/123,924, filed May 6, 2005, now U.S. Pat. No. 7,112,789 for“High Aspect Ratio, High Mass Resolution Analyzer Magnet and System forRibbon Ion Beams,” which claims priority to U.S. Provisional ApplicationNo. 60/571,965, filed May 18, 2004. Each of these applications is herebyincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The invention disclosed herein relates generally to apparatus forperforming ion implantation. Specifically, this invention relates to animproved implantation apparatus and methods for performing a high/mediumcurrent ion implantation at different ion energies.

BACKGROUND OF THE INVENTION

Ion implantation is a ballistic process used to introduce into a targetsubstrate atoms or molecules, generally referred to as dopants, to makematerials with useful properties. Of particular interest, ionimplantation is a common process used in making modem integratedcircuits. Ion implantation may also be used for thin film depositionwith controlled thickness and predefined surface properties formanufacturing optical or display devices such as flat panel displays.

FIG. 1 illustrates a conventional batch ion implantation system, of ageneral type which has been manufactured for about 30 years. Theimplantation system comprises an ion beam source 14 that forms an ionbeam 13. Beam 13 is directed to impinge on a batch of target substrates10 mounted on a disk-shaped target substrate holder 11. These elementsare housed in a vacuum housing which is not shown. The disk-shapedsubstrate holder is spun about axis 12 (which is preferably parallel tothe axis of beam 13) and translated horizontally so that the distance Rbetween axis 12 and beam 13 is varied. In order to achieve a uniformdose of ions, the translation velocity is inversely proportional to thedistance R.

In certain applications, particularly those using 300 mm wafers orlarger substrates as the implantation target, it is advantageous togenerate ion beams in the form of ribbon-shaped beams having high aspectratios such that the cross-section of the beam is much larger in onedimension than the other. These ribbon beams are commonly used in ionimplanter apparatus and implantation systems where a single workpiecesuch as a silicon wafer or flat panel display is moved in a singledimension through the ion beam. In these instances, the cross-section ofthe ribbon ion beam typically has one dimension that is larger than onedimension of the workpiece undergoing implantation. As a result, in oneor more passes through the ion beam, a uniform dose of ions may beimplanted into the workpiece.

In these applications, it is desirable that the ribbon beam have its iontrajectories moving in parallel and under careful control so as topresent a uniform current density profile that is appropriate for theimplantation of ions into semiconductor wafers or flat glass panels. Itis also desirable that the ion beam be substantially free of undesirablespecies that may be present in the ion source feed material and/or inthe materials of the source itself. For many years standard practice inthe industry has been to use magnetic analysis to separate and rejectany unwanted species or components from these ion beams. However, forlarge ribbon-shaped beams generally, this type of magnetic analysis andion beam purification becomes evermore difficult and costly. Thisparticular problem as well as the general state of the art of analyzingand transporting ribbon ion beams is reviewed in depth in White et al.,“The Control of Uniformity in Parallel Ribbon Ion Beams Up to 24 Inchesin Size,” Applications of Accelerators in Science and Industry 1998,AIP, p. 830, 1999, the entire text of which is expressly incorporated byreference herein.

Among the ion implanter apparatus and implantation systems commerciallyoffered for sale in recent years are those sold for ion beamimplantation of flat panel displays by Nissin Ion Equipment Co. Ltd.,Kyoto, Japan; Sumitomo Eaton Nova Corporation, Toyo, Japan; andIshikawajima-Harima Heavy Industries Co. Ltd., Tokyo, Japan. Most ofthese systems have little or no ability to reject unwanted speciecontaminants that are almost always present in the beam as it leaves theion source.

In contrast, Mitsui Engineering and Shipbuilding manufacturesimplantation apparatus and systems for commercial sale that are able toimplant flat panel displays with uniform ribbon beams which have beenmass analyzed (i.e., beams purified by the removal of undesirablespecies) using magnets having only modest resolving power (i.e.,approximately 2 power), which is often sufficient to remove theegregious specie contaminants from ion beams of several different,commercially useful source elements.

A type of ion implantation system for silicon wafers is represented bythe Models SHC 80, VIISta-80, and VIISta HC ion implantation systemsmanufactured by Varian Semiconductor Equipment Associates of Gloucester,Mass. This system is illustrated in FIG. 2 which is adapted from FIG. 1of U.S. Pat. No. 5,350,926, which is incorporated herein by reference.The system comprises an ion source 2 for generating an ion beam 1, ananalyzing electromagnet 3, a resolving aperture 4, and a secondelectromagnet 5. A control unit 36 receives beam intensity informationon line 36 a from a beam profiler and sends control signals along line36 b to control multipole elements in magnet 3 or along line 36 c tocontrol a beam trimmer. Magnet 3 mass analyzes the ion beam. Magnet 5expands the beam along the dispersive plane using magnetic fields inclosed loop control to maintain the uniformity of the beam. The resultis a ribbon-shaped ion beam 6 that is incident on target 7. Furtherdetails of the system of FIG. 2 are set forth in the '926 patent.

Due to the complex interactions between the ion beam and the magneticfield applied for beam expansion, this approach creates severetechnical, practical, and process related problems that increase thetotal production cost of such equipment and lead to more complicatedoperation procedures for carrying out the ion implantation. Inparticular, the beam path through this system is relatively long, and atlow energies and high beam currents it becomes increasingly difficult tocontrol the uniformity of the ion beam and the angular variation withinthe beam with the precision required by certain commercial processes.

It is further desirable to obtain milliampere currents of ions atenergies as low as 200 eV. The highest beam currents are obtained bydecelerating the ion beam immediately prior to the target. However thispractice has several known disadvantages. One disadvantage is that thedeceleration tends to modify the trajectories, magnifying any angularerrors and making control of uniformity in a ribbon beam more difficult.Another disadvantage is that a portion of the ions is neutralized bycharge-exchange processes with residual gas atoms and molecules and, asa result, is not decelerated. These ions penetrate into the silicon muchfurther than is intended, and this deep penetration of some of thedopant ions interferes with the intended process; furthermore, since itdepends on system pressure within the vacuum system, it is difficult tomaintain constant conditions from day to day, and the level ofcontamination is not sufficiently constant to be tolerated. The problemis well-known, and a solution is proposed in U.S. Pat. Nos. 6,489,622 B1and 6,710,358 B1, which are incorporated herein by reference.

As a result, these types of ion implantation systems often are not aviable solution for performing serial mode implantation with ahigh-current, high-uniformity ion beam that has controllable shapes andsizes. There is a need in the art of integrated circuit fabrication toprovide a new system configuration, for generating a high current ionbeam that has improved uniformity without requiring additionalcomponents while reducing the production cost and simplifying themanufacturing processes.

SUMMARY OF THE PRESENT INVENTION

One aspect of the present invention is an ion implantation apparatuscomprising an ion source, an extraction assembly for extracting an ionbeam through a divergent extraction-optics, a mass analyzer magnet and abeam density controller. The implantation apparatus further includes atarget chamber in which is mounted a target for implantation.Illustratively, the target is a semiconductor wafer or flat paneldisplay. The extraction-optics has a convex geometry to produce a beamthat is diverging as it leaves the extraction-optics. The ion beam isshaped by the divergent extraction-optics and the beam densitycontroller to have a relatively tall and narrow cross-section in whichthe longer dimension is located in the non-dispersive plane of themagnet. As the beam continues to travel, the beam continues to becometaller as it continues to diverge such that when the ion beam reachesthe target wafer, it has sufficient height to cover the entire diameterof the wafer. The apparatus for ion implantation further includes aFaraday beam current measurement device disposed in proximity to thetarget wafer for scanning across the longer transverse dimension of theion beam to measure the beam uniformity and to provide the measurementdata back to the beam density controller.

Another aspect of the present invention provides a single dipole magnet,which mass-analyzes the ion beam while allowing its major dimension tocontinue to diverge from the ion source in the direction of the dipolemagnetic field. It can additionally use a lens to halt the divergence ofthe ion beam on reaching the requisite major dimensional size andcollimate it, i.e. render it parallel. A suitable lens may use magneticor electric fields, may generate a quadrupole field, and must have abeam passage of high aspect ratio to conform generally to the ribbonshape of the ion beam.

In certain circumstances such as when using high-current low energybeams it may not be possible to assure a ribbon beam that issufficiently uniform. Another embodiment of this invention comprises anion source, which generates a ribbon-shaped ion beam, a magneticmass-analyzer, a focusing system for shaping the beam, and a processingstation where a workpiece such as a silicon wafer or flat-panel can bemechanically moved through the ion beam. As the ion beam leaves the massanalyzer, a first lens, which can be a magnetic multipole lenscomprising an array of pairs of coils arranged on a pair offerromagnetic supports, can be operated in two modes. In a first mode,the currents in the coils of this multipole lens can be controlledresponsive to a measurement of the ion beam profile to control thecurrent density in this beam profile. The ion beam is allowed tocontinue as a ribbon-shaped beam whose major dimension exceeds adimension of the workpiece. The workpiece is then translated throughthis ion beam along a single path, one or more times, to implant adesired uniform dose of ions into its surface. In a second mode, thecurrents in the coils of this first multipole lens are excited so as togenerate a quadrupole magnetic field which causes the ribbon ion beam toconverge in its major dimension, thereby generating at a downstreamlocation a beam spot which is smaller in both transverse dimensions thaneither dimension of the workpiece. The workpiece is then translated in areciprocating path in two dimensions through the ion beam, so as toimplant a uniform dose of ions into its surface by implanting asuccession of partially overlapping stripes.

The second mode is likely to be advantageous when using high-current,low-energy beams (for example greater than 1 mA at energies below 3 keV)under which conditions space-charge and other effects make positivecontrol of the uniformity of the current in a beam more difficult. Thefirst mode requires slower motions and is likely to deliver higherprocessing throughput at energies where satisfactory control of the ionbeam profile can be achieved. The currents in the multipole lens ineither mode may be adjusted to fine-tune the beam current densityprofile of the beam, even though at low energy this control isinsufficient to ensure a uniform implant in one pass with a ribbon beam.In the second mode, this may be valuable to approximate a smoothGaussian beam profile. Without a smooth beam profile, the method ofpassing the workpiece in regular increments through the ion beam maycause detectable stripes of varying ion beam dose in the workpiece.

A further aspect of the invention provides a second lens after the firstmultipole lens, whose function is to collimate the ion beam. This isparticularly important for the first operating mode, i.e. theribbon-beam case, where systematic variation in the implant angle acrossthe face of the workpiece would otherwise occur. It is also of value toreduce the range of angular variation in the ion beam in the secondmode.

A further aspect of the invention provides an optional means ofdeceleration of the ion beam using a bent ion beam path, to deliver highbeam currents at low energies while filtering out high-energycontaminants, for use in ion implantation in either the ribbon-beam or2D scan beam modes. In accordance with this aspect of the invention, thebeam is bent through an angle that differs by a small amount fromstandard conditions, then the ion beam is decelerated by means of a setof electrodes that superimpose two opposed successive sidewayscomponents of electric field on the deceleration field, so that the ionbeam is deflected in an S-shaped bend, the deflections each amounting toan angle of at least 10 degrees, and providing a lateral displacement ofseveral times the width of the ion beam. By providing beam stops oneither side of the beam, the only ions transmitted are those with thecorrect charge and energy, so contaminants such as high-energy neutralatoms can be removed.

The apparatus and methods of the invention make it possible:

-   -   1. To generate a ribbon beam for ion implantation which is        mass-analyzed efficiently with a single analyzing magnet in a        short, relatively simple beamline with high resolving power;    -   2. To provide a second operating mode where the beam can be        smaller than the target for implantation, and the target is        scanned in a 2D pattern to accomplish uniform implantation;    -   3. To control the collimation of the ion beam and control        variation in implantation angle over the surface of the target;    -   4. To provide a means of decelerating the ion beam in either        implantation mode in a manner which eliminates the usual        contamination with high-energy neutral atoms;    -   5. To provide a means of varying and controlling the current        density in the ion beam.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention will beapparent to those of ordinary skill in the art in view of the followingdetailed description in which:

FIG. 1 is a functional block diagram of a conventional prior art batchion implantation system in which a spinning disk holding implantationtargets provides one dimension of motion, and translation of the diskprovides a second dimension;

FIG. 2 is a functional block diagram of a prior art ribbon-beamimplanter in which the implantation target is translated though theribbon beam in one dimension;

FIG. 3 is a perspective view of a ribbon-beam system according to thepresent invention in which the ion beam diverges through an analyzermagnet and is then collimated by a lens;

FIGS. 4 a, 4 b and 4 c illustrate successive cross sections of a magnetwhich is tailored to fit an expanding ribbon beam;

FIG. 5 a illustrates an embodiment of the invention in which twomultipole lenses follow the analyzer magnet, and the beam has twopossible paths, one path passing through an s-bend where its isdecelerated to reach very low energies without contamination byhigh-energy neutral atoms or ions;

FIG. 5 b is a perspective view of the system of FIG. 5 a, showing thatthe scan system is capable of moving the target workpiece in twodimensions through the beam path;

FIG. 6 depicts the use of the embodiment of FIG. 5 to generate a narrowbeam taller than the target;

FIG. 7 depicts the use of the embodiment of FIG. 5 to generate a spotbeam smaller than the target;

FIG. 8 illustrates an apparatus for scanning the target through the ionbeam in either 1 or 2 dimensions;

FIG. 9 depicts the details of the s-shaped deceleration region used inthe system of FIGS. 5 a and b;

FIG. 10 illustrates an alternative prior art electrostatic lens thatcould be used in this invention for controlling the collimation of theion beam;

FIG. 11 illustrates the detailed construction of suitable magnet coils;and

FIG. 12 illustrates the detailed construction of a multipole lens.

DETAILED DESCRIPTION

FIG. 3 is a perspective view of a first embodiment of an ionimplantation system of the present invention. The system comprises anion source 102 that produces an ion beam 100 that emanates from adivergent extraction optics similar to those shown in FIG. 2, a massanalyzer magnet 414, and a collimator lens 200 As will be appreciated bythose skilled in the art, these elements are housed in a vacuumenclosure (not shown). Magnet 414 comprises upper and lower coils 120,121 and a yoke 110 with an entrance aperture 164 and an exit aperture166. The magnet is curved over an arc of about 90°. The cross-section ofthe ion beam is relatively tall and thin and the longer dimension of thecross-section lies in the non-dispersive plane of magnet 110. The ionbeam is slightly divergent upon exiting the extraction electrode; and asthe beam travels along the beam path, it continues to become taller asthe beam rays continue to diverge such that when it approaches thetarget (which may be a semiconductor wafer, for example) its majordimension is larger than the implantation target's size, i.e. 200 or 300mm for silicon wafers. The collimator lens 200 halts the divergence andrenders the beam parallel, controlling variation of implant angle acrossthe implanted surface of the target.

The analyzer magnet in FIG. 3 has a central passageway for the beam thathas a top and bottom that are parallel from entrance aperture 164 toexit aperture 166. Thus, a cross-section of the magnet taken along linesA-A′ of FIG. 3 at any point along the radius of curvature of the magnetis the same. However the ion beam is diverging. In a second embodiment,the construction of the magnet is modified as illustrated by the threecross sections in FIGS. 4 a, b, and c so that the height of the beampassage through the magnet increases as the beam expands. In particular,as shown in FIG. 4 a, which depicts a cross-section closest to theentrance aperture 164 of the magnet, the height of the centralpassageway 160 is smallest. As shown in FIG. 4 c, which depicts across-section closest to the exit aperture 166, the height of thecentral passageway is largest; and as shown in FIG. 4 b which depicts across-section between those of FIGS. 4 a and 4 c, the height isintermediate that of the other two. As a result, the beam occupies alarge fraction of the volume in which field is generated, and there isless waste of power in the generation of unused magnetic field.

A preferred embodiment of mass analyzer magnet 414 is shown in bothperspective views in FIGS. 6 and 11 and in cross-sections in FIGS. 4 athrough 4 c. The magnet comprises an arcuate yoke 110 of a ferromagneticmaterial and upper and lower coils 120 and 121. The yoke and coilsencompass a pathway for the ion beam that is curvilinear with a radiusof curvature in a range between 0.25 and 2 meters and an arc ofcurvature ranging from not less than about 45 degrees to not more thanabout 110 degrees. The yoke has a generally rectangular cross-sectionwith a top and bottom positioned at equal distances above and below theintended beam path, and vertical sides enclosing a spatial volumeencompassing the intended beam path. Coils 120 and 121 are saddle-shaped(also called bedstead-shaped) and are mirror images of one another inthe mid-plane. The magnetic field required to bend the ion beam isgenerated by current passing through the two coils. The direction of themagnetic field is generally vertical, and the magnetic field linesterminate on the top and bottom portion of the yoke normal to the insidesurfaces thereof.

Each of coils 120,121 comprises a winding or windings of conductive wirewhich is wound to fill an envelope of rectangular cross section whichfollows a three dimensional path. As shown in detail in FIG. 11, thepath of upper coil 120 comprises multiple segments as follows:

-   -   a segment 120 a commencing to the right of the intended beam        axis at the entrance of yoke 310, taking a arcuate path        generally parallel with the intended beam axis to the exit of        the yoke, passing between a sidewall of the yoke and the        intended beam path,    -   a segment 120 b curving approximately 90 degrees upwards,    -   a segment 120 c arching to the left over the top of the beam        path through approximately 180 degrees close to the exit of the        yoke (this segment may optionally be subdivided into two        arc-shaped segments and a straight section),    -   a segment 120 d curving through approximately 90 degrees towards        the exit of the yoke,    -   a segment 120 e commencing at the exit of the yoke and taking an        arcuate path generally parallel to the intended beam axis as far        as the entrance of the yoke, in the opposite direction to the        intended travel of the beam, passing between a sidewall of the        yoke and the intended beam path,    -   a segment 120 f curving upwards through approximately 90        degrees,    -   a segment 120 g arching to the right over the top of the beam        path through approximately 180 degrees close to the entrance of        the yoke (this segment may optionally be subdivided into two        arc-shaped segments and a straight section), and    -   a segment 102 h curving 90 degrees towards the entrance of the        yoke, and joining onto the beginning of the path of the coil        envelope, so as to complete a circuit.        As noted above, the lower coil is a mirror image of the upper        coil.

Thus, the pair of saddle-shaped coils:

-   -   (i) presents a bend direction for the two rounded inclined ends        of one looped-shaped coil which is opposite to the bend        direction for the two rounded inclined ends of the other        looped-shaped coil in the array,    -   (ii) provides a central open spatial channel via the cavity        volume of the closed loop in each of the two coils, said central        open spatial channel extending from each of said inclined loop        ends to the other over the linear dimensional distance of the        array,    -   (iii) is positioned within said internal spatial region along        the interior surfaces of two opposing walls of said arcuate yoke        construct such that one pair of aligned rounded inclined loop        ends extends from and lies adjacent to each of the two open ends        of said arcuate yoke construct, and    -   (iv) serves as limiting boundaries for said curvilinear central        axis and intended arc pathway for the continuous ribbon ion beam        as it travels in the gap space existing between said two        loop-shaped coils positioned within said internal spatial region        of said arcuate yoke construct.

The rectangular envelope along the path so described is filled bywinding a predetermined number of turns of conductor along it. The coilso formed may optionally be impregnated with resin to form a rigid body.The lower coil is formed in a similar way to the upper coil. Both coilsmay be connected in series to a source of current, or two sources ofcurrent, one for each coil, may be used. The arcuate part of theintended beam path is enclosed on the left and right by segments of theupper and lower coils, and at the top and bottom by steel parts of theyoke. The effect of passing electrical current through the coil is togenerate a substantially uniform vertically oriented magnetic fieldwithin the enclosed volume bounded by the coils and the top and bottomof the yoke, and to provide regions at the entrance and exit in whichthe magnetic field falls rapidly with distance from the yoke to a nearzero value. The magnetic field as a whole is effective to deflect aribbon-shaped ion beam along an intended path, and through an aperture,rejecting contaminants. The mid-plane of the magnet 214 and thenon-dispersive plane extends from the ion source to the targetperpendicular to the dispersive plane.

A preferred embodiment of collimator lens 200 is shown in FIG. 12 whichis adapted from FIG. 7 of U.S. patent application Ser. No. 10/807,770,filed Mar. 24, 2004, now U.S. Patent Application Publication No.2005/0017202 for “Electromagnetic Regulator Assembly for Adjusting andControlling the Current Uniformity of Continuous Ion Beams.” Thisapplication is incorporated herein by reference in its entirety. Asshown in FIG. 12, collimator lens 200 comprises two ferromagnetic bars1120 and 1220, each of which is sized to be somewhat longer in linearlength than the x-dimension of the traveling ion beam intended to becontrolled; and is oriented to lie parallel to and at a pre-chosen gapdistance 1144 from one another. Each ferromagnetic bar 1120 and 1220serves as a straight supporting rod around which a plurality ofindividual wire coils 1122 and 1222 are orthogonally wound at a numberof predetermined and different locations; and collectively create anaxially aligned series of independent, separated, and adjacently locatedcoiled windings.

A component part of the collimator lens is on-demand means (not shown)for introducing electrical energy of variable current (amperes)independently through each independent and adjacently positioned wirecoil 1122 and 1222 which is orthogonally disposed along the fixed lengthof the support rods 1120 and 1220. Given the flow of electrical energyof an appropriate current, each adjacently positioned and energized wirecoil 1122 and 1222 independently generates an orthogonally extending andindividually adjustable magnetic field gradient of limited breadth; andthe plurality of adjacently extending magnetic field gradients oflimited breadth collectively merge to form a contiguous magnetic field;and the strength of each magnetic field of limited breadth within thecontiguous magnetic field can be individually altered at will by varyingthe electrical current to yield an adjustable and controllable magneticfield gradient over the contiguous magnetic field.

In particular, as illustrated in FIGS. 2 and 3 of the '770 applicationand as described in conjunction with FIGS. 6 and 7 below, the windings1122, 1222 can be selectively excited so as to alter the shape and/oruniformity of the ion beam. Thus, the current density profile of the ionbeam can be altered so as to produce at a workpiece a beam profileapproximating any one of the following profiles:

-   -   a uniform profile extending across a dimension of the workpiece    -   a Gaussian profile or other desired profile    -   a linearly varying profile extending across a dimension of the        workpiece or    -   any other pre-defined beam profile useful in an ion beam        process. Moreover, in the case of the Gaussian beam profile and        other profiles for which measures such as half-width have        meaning, the half-width for the beam profile can be controlled.

In a preferred embodiment of the invention shown in FIG. 5 a, the ionimplantation system comprises an ion source 410, extraction optics 412,an analyzer magnet 414, a focusing system 430, a controller 440, atarget chamber 450 and a wafer transport system 475. The implantationsystem also comprises beam dumps 505 for absorbing unwanted ions and aFaraday beam profile measurement system 420 located in target chamber450.

The ion source 410 preferably is a Bernas-type ion source and theextraction optics have a slightly convex shape. Mass analyzer magnetpreferably is the same as that of the system f of FIG. 3 which isdescribed in detail in paragraphs 0039 to 0056 above. The focusingsystem 430 further comprises a first set of multipole magnets 402 and asecond set of multipole magnets 404. Each set of multipole magnets has aconstruction similar to that of collimator lens 200 of the system ofFIG. 3. The construction of such multipole magnets is described in moredetail in paragraphs 0057 and 0058 above and in the above-referencedU.S. patent application Ser. No. 10/807,770. The operation of thefocusing system is described above in paragraphs 0059 to 0063. Targetchamber 450 (FIG. 5 a) also includes an electrostatic chuck 471 and atranslation stage for moving the mounting in two directions. In FIG. 5a, these directions typically are up and down relative to the mid-plane(i.e., in and out of the plane of the paper) and left and right of thenon-dispersive plane (i.e., up and down in the plane of the paper). Thewafer transport system 475 further comprises load locks 474 aand 474 b,and a robot arm 475 a for moving a wafer from one load lock to thetransport mechanism for ion implantation and for moving an implantedwafer from the transport mechanism to a load lock.

Further details of a preferred mechanical two-dimensional scanningsystem for the workpiece are shown in FIG. 8 which is adapted from FIG.10 of U.S. Patent Application Publication No. US2005/0173656 A1 which isincorporated by reference herein in its entirety. An electrostatic chuck471 for the workpiece 460 is mounted on an arm 472, and the arm ispivoted about a horizontal axis 490, situated 900 mm in this instancefrom the center of the workpiece, and parallel to the beam axis 501.With the arm swung to position the chuck at one side of the ion beampath, a second axis of rotation allows the chuck to pivot to ahorizontal position, allowing a robot arm 475 a to transfer workpiecesoff and on the chuck from loadports 474 a or 474 b. Once a workpiece isloaded onto the chuck, the chuck is rotated about the horizontal axis490 until the normal to the workpiece surface is at a predeterminedangle to the beam axis 501 (commonly 0°).

If a ribbon beam is used, the height of the arm is adjusted by a linearmotor (not shown) sliding the mechanism along a sliding seal 480, untilthe workpiece trajectory is centered on the beam, at which point the armcan be rotated at a controlled velocity about axis 490, back and forthas required, passing the workpiece through the ribbon beam to implant adesired dose of ions into the workpiece.

To carry out an implant with a two-dimensional scan, the arm is moved tothe bottom of its travel on sliding seal 480, then its height isincreased progressively as the arm is pivoted to and fro to pass theworkpiece through the beam (which is focused to a spot smaller than theworkpiece in this case) in a curved zig-zag pattern, so as to implant auniform dose of ions into the workpiece.

In operating the system of FIG. 5 a, the Bernas-type ion source 410 isused to produce an ion beam 400 that is much taller than it is wide. Aset of extraction optics 412 is used to extract the ion beam by applyinga relative negative potential on the first electrode. The emergent beamhas slightly divergent ray paths with respect to the non-dispersiveplane of the magnet 414. As a result, a ribbon-shaped beam is producedhaving a rectangular cross-section with a longer dimension that lies inthe non-dispersive plane. The ion beam is directed into mass analyzermagnet 414 which selects the desired ions with the appropriate charge tomass ratio. The desired ions then traverse the first set of multipolemagnets 402 that is controlled in either open or closed loop operationvia feedback from the Faraday beam profile measurement system 420. Thefirst set of multipole magnets 402 is operated in response to ameasurement of the beam profile by Faraday measurement system 420 tocontrol the size and current density profile of the beam to insure thatthe amount of total ion dose rate per unit height will be uniform at thepoint of use, i.e. the target wafer 460. To do this, the coils of thefirst set of multipole magnets generate an overall quadrupole field withsuperimposed controllable regions of field gradient. After the ion beampasses through the first set of multipole magnets 402, it continuesalong the beam path to the second set of multipole magnets 404. Thecoils of the second set of multipole magnets can also be used togenerate a quadrupole field that as described below is suitable forcollimation of the ion beam in the non-dispersive plane of the analyzermagnet 414, thereby canceling the divergence or convergence of the ionbeam. The coils of the second set of magnets can also be used tosuperimpose further controllable regions of field gradient to reduceangular variations in the beam, including variations generated by thefirst set of magnets 402. The desired ions pass through a selected gapbetween the poles of this lens; and beam dumps 505 of a suitablematerial block all other paths for any stray beam ions, so that only thedesired ions can reach the target chamber 450. The target 460 can bemechanically scanned in a direction perpendicular to the beam and in theplane of the paper so as to provide uniform implantation coverage of thetarget.

The ion implantation system of FIGS. 5 a and 5 b can be operated in twomodes depicted in FIGS. 6 and 7. FIGS. 6 and 7 depict the system ofFIGS. 5 a and 5 b in greatly simplified form for ease in understandingthis aspect of the invention. Specifically, only mass analyzing magnet414, focusing system 430 with the first and second sets of multipolemagnets 402, 404, controller 440, and target 460 are shown.

In the first mode of operation illustrated in FIG. 6, the ion beam isallowed to continue as a ribbon-shaped beam whose major dimensionexceeds a dimension of the workpiece. Thus, focusing lens 430 isoperated in the first mode so that the ion beam is allowed to expanduntil it reaches a size greater than that of target 460. The currents inthe coils of the second set of multipole magnets 404 are controlledresponsive to a measurement of the ion beam profile to control thecurrent density in this beam profile. In particular, the currents areused to collimate the ion beam so that the ions in the beam aresubstantially parallel as the beam is directed onto the target 460 inchamber 450. The workpiece is translated through this ion beam along asingle path, one or more times, to implant a desired uniform dose ofions into its surface. Illustratively, the workpiece may simply be movedlaterally through the beam, as illustrated by the arrows in FIG. 6.However, in the embodiment shown in FIGS. 5 a and 5 b, it is moved on anarc-shaped path, and this requires that the beam uniformity becontrolled so that the current density within the beam is proportionalto the local scan velocity of the target workpiece, which isproportional to distance from the pivot axis of the arm.

While implant operations with such a ribbon beam provide high throughputin an ion implantation operation, it is difficult if not impossible toensure adequate uniformity of the ion beam at high currents andextremely low ion energies such as those needed in the manufacture ofmodem integrated circuits. In particular, for currents in excess of 1 mAand ion energies less than about 3 keV, even with care to establishspace-charge neutralization, space charge effects can cause enoughdisruption of the ion beam to make it impossible to assure that a ribbonbeam has the uniformity required for ion implantation of semiconductorwafers.

In this situation, focusing lens system 430 is operated in a second modeillustrated in FIG. 7 so as to focus the ion beam to a smallercross-section beam 701 than the implant target. More particularly, inthe second mode, the currents in the coils of the first set of multipolemagnets 402 are excited so as to generate a quadrupole magnetic fieldwhich causes the ribbon ion beam to converge in its major dimension,thereby generating at a downstream location a beam spot which is smallerin both transverse dimensions than either dimension of the targetworkpiece 460. Again, the second set of multipole magnets 404 is used toreduce the range of angular variation in the ion beam. In the secondmode of operation, the workpiece is translated in a reciprocating pathin two dimensions through the ion beam, so as to implant a uniform doseof ions into its surface. Illustratively, the target is scanned in twodimensions both up and down relative to the mid-plane and left and rightacross the non-dispersive plane to ensure that the reduced size ion beamirradiates the entire semiconductor wafer target.

Advantageously, the two modes of operation of the multipole lens areachieved by applying different currents to the individual coils of thesets of magnets 402, 404 under control of a system controller 440.Simultaneously, the controller also controls the operation of thetranslation stage so as to provide for a one-dimensional ortwo-dimensional scan.

A preferred embodiment of the invention uses alternative ion beam paths501, 502 after the analyzing magnet, as shown in FIG. 5 a. Such pathsfacilitate the delivery of higher beam currents at lower energies forion implantation in either mode of operation of focusing system 430. Theanalyzer magnet is adjusted to deflect the ion beam from its initialaxis 501 through an additional five degrees onto axis 502, which can beseen to incorporate an s-bend and re-merge with axis 501. In the courseof passing along this axis, the ion beam is decelerated to apredetermined energy in the approximate range from 3% to 20% of theinitial energy. To accommodate this change, the first set of multipolemagnets 402 can be moved on a track as indicated by arrow 403 to becentered on this modified beam axis 502, and where the ion beam passesthrough the second set of multipole magnets 404 a second beam channel isprovided, in which the direction of the magnetic field is convenientlyreversed from its direction on axis 501. Other methods and variations ofthis method of providing for a suitable second beam path are alsoenvisioned.

After passing through these focusing devices, as shown in greater detailin FIG. 9, the beam passes through a short region of acceleratingelectric field prior to being decelerated. Ion beam paths 901 and 902 ofFIG. 9 correspond to ion beam paths 501 and 502 of FIG. 5 a. A first setof electrodes 910 define the initial energy a second set of electrodes911 a-c are at a more negative voltage to suppress electrons, a thirdset of electrodes 912 a, 912 b are at an intermediate positive potentialand a fourth set of electrodes 913 are at the final potential.Illustratively, in FIG. 9, a 10 mA beam of boron ions is initiallytraveling at 4 keV. The suppression potential is approximately −3 keV,and the potential difference between electrodes 510 and 513 is 3800V.

The function of the negative suppression potential on electrodes 911 a-cis well-known: to prevent electrons within the ion beam from beingaccelerated in the ion deceleration region. Following the suppressionregion, a positively biased electrode 912 a is placed on one side of theion beam. It has two functions: to create a deflection field, and toraise the potential on the beam axis, thereby partially decelerating thebeam. After the beam has been deflected left through about 20 degrees itpasses through a restricting aperture formed by electrodes 910 r. Theamount that the beam is deflected can be adjusted and controlled byvarying the suppression potential on electrodes 911 a and 911 b. Afterpassing though this aperture the beam is strongly decelerated whilebeing deflected to the right, so as to merge with the initial beam path.The final beam energy is defined by the potential between the ion sourceand the implant target. The final electrodes 913 are at the potential ofthe implant target, but are shaped so as to create a bending field aswell as deceleration. Electrode 913 m is movable as indicated by thearrows, and adjustment of its position is useful in adjusting the ionbeam to precisely merge with the original beam axis 901, but at a smallfraction of the original energy. Neutral atoms within the ion beam uponarrival at the deceleration structure are not deflected and arecollected in a neutral beam dump. Ions which undergo charge exchangewhile passing through this s-bend structure will largely also exit thebeam. Upon exiting the structure of FIG. 9, there is only a short, smallregion in which it is possible to charge-exchange an ion in a mannerthat would permit it to reach the wafer.

Experimentally it has been found that a) the level of energycontamination within a 200 to 500 eV ion beam may be reduced below0.05%, b) the maximum energy present within this beam is no more thandouble the final energy although the beam may have been decelerated froman energy 10 to 20 times the final energy, and c) beam currents ofalmost pure low energy beams are many times greater than those currentlyavailable form other types of implantation equipment.

The use of this s-bend deceleration in the second mode of the beamlinemeans that 2-dimensional scanning may be used to obtain a uniformimplant dose and that simultaneous accurate control of the uniformity ofthe ribbon beam is no longer necessary.

Another embodiment of this invention uses electrostatic lenses insteadof magnetic lenses in focusing system 430 to collimate or focus the ionbeam. An example of such lenses is shown in FIG. 10 which is adaptedfrom FIG. 2 of U.S. patent publication 2004/0262542 A2 which isincorporated herein by reference. A first pair of electrodes 1061, 1062establish a first voltage gap and a second pair of electrodes 1063, 1064establish a second voltage gap. Slot-shaped openings in the electrodesallow an ion beam 1048 to pass through. As described more fully inparagraphs 0021 and 0022 of the '542 publication, the action of theelectric fields set up by the electrodes cause ions that enter the lensto exit the lens on trajectories generally parallel to axis 1048.

The ion implantation system of this invention has significant advantagesover prior art ion implantation systems. Serial-mode implantation ispreferable to batch-mode for throughput considerations and reduced riskin product loss in the event of machine failure. Serial ion implantationsystems also have much simpler and less expensive wafer handling systemsso that development, manufacturing, and operating costs are lower thanbatch-mode systems. By implementing the system design and configurationof this invention, equipment suppliers can meet the challenge of makinga serial machine for implantation applications that is reliable and hascompetitive process control capability. Furthermore, the novel systemconfiguration as now taught by this invention involves relatively fewcomponents compared to other serial high current methods, which have yetto achieve any notable success. Currently batch mode machines arefilling the high current implanter niche but this invention provides asuperior product to the semiconductor industry, especially for lowenergy and 300 mm applications.

In addition to ion implantation, the process and apparatus of thepresent invention may also be used for film coating or carrying outother types of surface processing applications. As the beam is projectedas a divergent beam with small divergent angle, a highly uniform beamdensity is provided for implantation or depositing particles to achievehigher level of uniformity as the expanded beam reaches the targetsurface. As a result, the invention finds application for deposition ona surface to form optical filter coatings or for different types ofsurface processing functions on glass, metals or a wide variety ofmaterials.

Although the present invention has been described in terms of severalembodiments, it is to be understood that such disclosure is not to beinterpreted as limiting. Various alterations and modifications will nodoubt become apparent to those skilled in the art after reading theabove disclosure. Accordingly, it is intended that the appended claimsbe interpreted as covering all alterations and modifications as fallwithin the true spirit and scope of the invention.

1. Apparatus for implanting a target with ions, comprising: an ion source; extraction optics for extracting from the ion source an ion beam that projects with a slightly divergent angle from an ion beam axis; and a magnetic mass analyzer for guiding the ion beam along a trajectory according to a mass-to-charge ratio, wherein the magnetic mass analyzer comprises: an arcuate yoke encompassing a pathway for the ion beam; and a mirror symmetrical pair of saddle-shaped coils extending through the yoke along the ion beam pathway wherein each saddle-shaped coil comprises eight connected conductive segments in sequential series including; a first curved segment lying generally parallel to a curved segment of the beam axis, tangential to a midplane of the beam axis; a second curved segment bending about 90° degrees away from the midplane of the beam axis; a third curved segment of 180° arching across the beam axis; a fourth curved segment of about 90° angle lying generally parallel to the second segment; a fifth curved segment lying parallel to the curved beam axis segment and opposite to the first segment; a sixth segment bending 90° away from the midplane of the beam axis; a seventh segment arching back through 180° across the beam axis; and a eighth segment turning 90° and connecting to the first curved segment wherein the ion beam diverges to form a continuous ribbon beam having a longer dimension in a non-dispersive plane of the magnetic mass analyzer.
 2. Apparatus for implanting a target with ions, comprising: an ion source; extraction optics for extracting from the ion source an ion beam that projects with a slightly divergent angle from an ion beam axis; and a magnetic mass analyzer for guiding the ion beam along a trajectory according to a mass-to-charge ratio; wherein the magnetic mass analyzer comprises: an arcuate yoke encompassing a pathway for the ion beam, said pathway being curvilinear with a radius in a range between 0.25 and 2 meters and an arc of curvature ranging from not less than about 45 degrees to not more than about 110 degrees; said arcuate yoke being formed at least in part of a ferromagnetic material and comprising an arcuate wall structure having fixed dimensions and substantially rectangular cross-section, two discrete open ends which serve as an entrance and exit for the traveling beam, and an internal spatial region of determinable volume which serves as a spatial passageway for the traveling beam; a mirror symmetrical pair of saddle-shaped coils set in parallel as an aligned array, (a) wherein each discrete coil of the pair in the aligned array is an elongated complete loop having two rounded and inclined loop ends, each of which is bent in the same direction, and two sets of multiple conductive segments connecting the loop ends on opposite sides of the internal spatial region, and (b) wherein the aligned array of two saddle-shaped coils paired in mirror symmetry (i) presents a bend direction for the two rounded inclined ends of one looped-shaped coil which is opposite to the bend direction for the two rounded inclined ends of the other looped-shaped coil in the array, (ii) provides a central open spatial channel via the cavity volume of the closed loop in each of the two coils, said central open spatial channel extending from each of said inclined loop ends to the other over the linear dimensional distance of the array, (iii) is positioned within said internal spatial region along the interior surfaces of two opposing walls of said arcuate yoke construct such that one pair of aligned rounded inclined loop ends extends from and lies adjacent to each of the two open ends of said arcuate yoke construct, and (iv) serves as limiting boundaries for said curvilinear central axis and intended arc pathway for the continuous ribbon ion beam as it travels in the gap space existing between said two loop-shaped coils positioned within said internal spatial region of said arcuate yoke construct, wherein the ion beam diverges to form a continuous ribbon beam having a longer dimension in a non-dispersive plane of the magnetic mass analyzer.
 3. The apparatus of claim 1 further comprising a multipole lens for controlling uniformity of the ribbon beam.
 4. The apparatus of claim 2 further comprising a multipole lens for controlling uniformity of the ribbon beam.
 5. The apparatus of claim 1 further comprising a collimating lens for controlling collimation of the ion beam.
 6. The apparatus of claim 2 further comprising a collimating lens for controlling collimation of the ion beam. 